return readable store directly form derived, avoid .shift()

src/runtime/store/index.ts

@@ -71,17 +71,16 @@ export function writable<T>(value: T, start: StartStopNotifier<T> = noop): Writa
 			value = new_value;
 			if (stop) { // store is ready
 				const run_queue = !subscriber_queue.length;
-				for (let i = 0; i < subscribers.length; i++) {
+				for (let i = 0; i < subscribers.length; i += 1) {
 					const s = subscribers[i];
 					s[1]();
 					subscriber_queue.push(s, value);
 				}
 				if (run_queue) {
-					let s;
-					while (s = subscriber_queue.shift()) {
-						const val = subscriber_queue.shift();
-						s[0](val);
+					for (let i = 0; i < subscriber_queue.length; i += 2) {
+						subscriber_queue[i][0](subscriber_queue[i + 1]);
 					}
+					subscriber_queue.length = 0;
 				}
 			}
 		}
@@ -141,7 +140,7 @@ export function derived<T, S extends Stores>(
 
 	const auto = fn.length < 2;
 
-	const store = readable(initial_value, (set) => {
+	return readable(initial_value, (set) => {
 		let inited = false;
 		const values: StoresValues<S> = [] as StoresValues<S>;
 
@@ -182,10 +181,4 @@ export function derived<T, S extends Stores>(
 			cleanup();
 		};
 	});
-
-	return {
-		subscribe(run: Subscriber<T>, invalidate: Invalidator<T> = noop): Unsubscriber {
-			return store.subscribe(run, invalidate);
-		}
-	};
 }